A conventional portable device system performs encrypted communication between a vehicle and a portable device, which a user of the vehicle carries, and permits or performs locking or unlocking of a vehicle door and the starting or stopping of the engine when the verification is successful. The communication between the portable device and the vehicle is encrypted and protected (for example, refer to patent document 1).
As the above encrypted communication, the common key cryptosystem that uses the same encryption key for encryption and decryption is known. A common encryption key, that is, the same encryption key is registered to a portable device and a vehicle, which perform encrypted communication using the common key cryptosystem. The encryption key is registered to the portable device and the vehicle when registering the portable device to a controller of the vehicle. The controller verifies the portable device by verifying identification information that is received through radio communication from the portable device with identification information that is stored in the controller.